Acceleration of vulcanization by means of nu-ethyl-2-thiazoline sulfenamide



United States Patent ACCELERATION OF VULCANIZATION BY MEANS OFN-ETHYL-2-THIAZOLINE SULFENAMIDE Edward L. Carr, Akron, Ohio, assignorto The Firestone Tire & Rubber Company, Akron, Ohio, a corporation ofOhio No Drawing. Original application April 30, 1949, Serial No. 90,772.Divided and this application December 7, 1953, Serial No. 402,130

2 Claims. (Cl. 260-795) This invention relates to the vulcanization ofrubber or the like by use of a new class of accelerators.

This application is a division of my co-pending application Serial No.90,772, filed April 30, 1949, which was in turn a continuation-in-partof application Serial No. 586,039, filed March 31, 1945, now abandoned.

An object of the invention is to provide an improved process ofvulcanizing a rubber or synthetic rubber. Another object is to provide avulcanizable rubber composition capable of rapid vulcanization atcustomary rubber curing temperatures, but free from the danger ofsetting-up during factory processing operations. The above and furtherobjects will be manifest in the description of the invention whichfollows.

The new class of accelerators of this invention possesses the followingformula:

wherein R is an alkyl or cycloalkyl radical. The invention includesthiazoline-Z-sulfenamides of the above structure in which R isisopropyl, sec. butyl, sec. amyl, sec. hexyl, sec. octyl, cyclohexyl,methylcyclohexyl, decyl, dodecyl, hexadecyl, methyl, ethyl, propyl,namyl, tert. butyl, n-heptyl, and similar alkyl and cycloalkyl radicals.

The following examples are given to illustrate the new class ofaccelerators and methods by which they may be synthesized.

EXAMPLE 1 A 3.3 molar aqueous solution of sodium thiazoline-Z-mercaptide was prepared by dissolving Z-mercaptothiazoline in aqueoussodium hydroxide. An aqueous suspension of chloro-isopropylamine wasprepared by adding 2.5 molar sodium hypochlorite solution toisopropylamine maintained at C. The mercaptide solution was thengradually added, with stirring, to the aqueous suspension of thechloro-amine at a reaction temperature of 0 C. The molar ratio of amineto hypochlorite to mercaptide was 1.25 to 1.15 to 1.00 in thispreparation. The reaction product, N-isopropylthiazoline-Z-sulfenamide,separated as a white, crystalline substance, melting at 28.0-28.5 C. Thestructure of the product was proved by the following analytical results:

Calculated for CsHrzNaSa: N, 15.89%; S, 36.38%. Found: N, 15.91%; S,36.52%.

EXAMPLE 2 An aqueous suspension of chloro-sec. amylamine was prepared byadding 2.5 molar sodium hypochlorite solution to sec. amylaminemaintained at 0 C. A 3.3 molar aqueous solution of sodiumthiazoline-Z-mercaptide was then gradually added, with agitation, to thechloro-amine suspension at a reaction temperature of 0 C. The molarratio of reagents was the same as in Example 1. The reaction product,N-sec. amylthiazoline-Z-sulfenamide, separated as a dark amber liquid,analyzing as follows:

Calculated for CsHmNaSz: N, 13.7%; S, 31.3%. Found: N, 12.7%; S, 29.7%.

EXAMPLE 3 An aqueous suspension of chloro-cyclohexylamine was preparedby adding 2.5 molar sodium hypochlorite soution to cyclohexylaminemaintained at 0 C. A 3.3 molar aqueous solution of sodiumthiazoline-Z-mercaptide was then gradually added, with stirring, to thechloro-amine suspension at a reaction temperature of,

0 C. The molar ratio of reagents was the same as in Example 1. Thereaction product, N-cyclohexylthiazoline-Z-sulfenamide, separated aswhite crystals, melt-v mg at 69-70 C. The structure of the product wasproved by the following analytical results:

Calculated for CsHmNzSz: N, 12.95%; S, 29.64%. Found N, 13.00%;S,'29.60%.

EXAMPLE 4 Formula I 7 Rubber 100.0 Antioxidant 2.0 Pine tar 2.0 Carbonblack (E. P. C.) 45.0 Stearic acid 4.0 Zinc ox 2.5 Sulfur I 2.5Accelerator 1.0

Two rubber compositions were mixed in a conven tional manner, inaccordance with Formula I, to provide vulcanizable compositionsdiffering only in the accelerator employed. Separate portions of the,two'compositions were heated at 280 F. for 30, 60 and minutes, and thevulcanized compositions so produced were found to possess the followingphysical properties.

TABLE I Modulus at 400% Tensile Strength Accelerator produced in elonatlon in t b ak accordance w1th lbgalmz 8 i (Cure in minutes) 3O 60 9030 60 Example 1 2, 2, 600 2, 775 3, 825 3, 475 3, 700 Example 2 775 1,500 1,950 2, 575 3, 400 3, 725

Formula II Parts by weight Rubber 100 Sulfur 3 Stearic acid 1.10 Zincoxide 5 Accelerator 0.75

The rubber composition containing the cyclohexyl de rivative was mixedin the usual manner and then sep arate portions were heated for 30, 60and minutes at 240 F. and at 20, 40, 60 and 100 minutes at 280 F.Likewise, a control composition, containing as an accelerator theconventional mercaptobenzothiazole,

Patented Jan. 25, 1955.

was mixed and then heated under the same conditions as the compositioncontaining the cyclohexyl derivative of the invention. The physicalproperties of the two sets of heat-d rubber composltions are giveninTable II.

. 4 and acrylonitrile, rubbery copolymers of isobutene and butadiene orisoprene, and various other known polymers, copolymers, terpolymers,etc. produced from monomers at least one of which is a conjugated diene.

The invention comprehends the acceleration of sul- The data presented inTable II show that the accelerators of the invention are very effectivein a gurutype rubber formula to provide rapid vulcanization at customarycuring temperatures (e. g. 280 F.), producing vulcanizates having highmodulus and tensile properties. These data also show that the newaccelerators are delayed-action accelerators, since the compositioncontaining the cyclohexyl derivative was entirely unvulcanized after aminute heating period at 240 F., whereas the mercaptobenzothiazolecomposition was partially vulcanized (well set-up) after this shortheating period. This result means that the accelerators of the inventionmay be used to provide rapid curing rubber compositions which are freefrom the usual tendency of such vulcanizable compositions to set-upduring factory processing thereof, as during mill or Banbury mixing,calendering and extruding operations.

The vulcanizates produced in accordance with the invention possessexcellent resistance to deterioration upon aging or flexing thereof, andthey also exhibit low hysteresis properties. Thus, the vulcanizates aresu' perior in pneumatic tire bodies, sidewalls and treads. Because oftheir freedom from tendency to scorch or set-up during processing, andalso because of their rapid curing properties at tire vulcanizingtemperatures, the vulcanizable compositions of the invention are highlydesirable in chafer stocks and tire bead stocks.

The various synthetic rubbers susceptible to vulcanization by sulfur areequivalent to natural rubber. in this invention. Such synthetic rubbersinclude GR-S (rubbery copolymers of butadiene or isoprene with styreneor substituted styrenes), rubbery butadiene and isoprene polymers,rubbery copolymers of butadiene fur vulcanization whether the sulfur ispresent in the rubber composition as free sulfur or chemically boundsulfur available for vulcanization, as may be provided by the so-calledsulfur donors.

Examples of a few known sulfur donors are the following substances:

Tetramethylthiuram disulfide Polysulfides of phenolsand cresols Diethylxanthogen disulfide Polyethylene polysulfides The accelerators of theinvention are usually employed in the range of 0.5 to 2.0% by weight ofthe rubber in the vulcanizable composition, but they are useful in thebroader range of 0.1 to 10%. Since the 40 new accelerators are veryefiicient at the ordinary vulcanizing temperatures of 250-400 F., theydo not require further activation for most purposes. However, they maybe used in combination with one or more additional conventionalaccelerators and/or activators to provide special vulcanizablecompositions displaying unusually rapid or critical vulcanizingproperties and to produce vulcanizates exhibiting superior physical andchemical properties desired for special applications.

What is claimed is:

l. The process of vulcanizing rubber which comprises heating rubber andsulfur in the presence of a small quantity of N-ethyl-Z-thiazolinesulfenamide.

2. The vulcanized rubber product obtained by heating rubber and sulfurin the presence of a small quantity of N-ethyl-Z-thiazoline sulfenamide.

No references cited.

1. THE PROCESS OF VULCANIZING RUBBER WHICH COMPRISES HEATING RUBBER AND SULFUR IN THE PRESENCE OF A SMALL QUANTITY OF N-ETHYL-2THIAZOLINE SULFENAMIDE. 